What is the meaning of the numbers and letters in parenthesis for chess openings. example: Queens Pawn (A40)?

Question

another example: English Opening (A10); Reti Opening (A04)

Answer 1

There is no specific meaning to them. In 1966, Chess Informant categorized the chess openings into five broad areas ("A" through "E"), with each of those broken down into one hundred subcategories ("00" through "99"). The openings were published in five volumes of Encyclopaedia of Chess Openings, with volumes labeled "A" through "E".

Answer 2

Just to add to what Thomas W posted, the ECO codes help players identify the variations of the various openings. If I'm thumbing through a book or magazine that uses those codes, I can instantly see the particular variation played in that game. Since I'm familiar with the ECO codes for the openings I play, it saves me a lot of time reading through the moves to see which variation was played in the game. It's simply not possible to play over every game one comes across, so being able to see at a glance that the game is a Sicilan variation, Keres Attack, B81, is a big timesaver.

Answer 3

cordnites